The present invention relates to a color image forming apparatus such as a color printer, a color copier and the like. The present invention especially relates to a color image forming apparatus which can form a color image of stable quality, be made compact, and meet the demand of forming a black and white image. Furthermore, the present invention relates to a color image forming apparatus that enables formation of a stable black and white image and which is in great demand.
It is also the principal object of this invention to provide an improved electrostatic color image forming apparatus in which: a photoreceptor drum and a developing unit are assembled into a cartridge so that the cartridge can be rapidly attached to and removed from the apparatus in order to easily clean and inspect the inside of the apparatus; and the cartridge can be easily and positively replaced with a new one when the cartridge has been used to the limit defined as the predetermined number of times in which image forming is conducted.
For example, a copier with a process cartridge has been disclosed in Japanese Patent Publication Open to Public Inspection No. 163276/1982, wherein the process cartridge is integrally composed of a photoreceptor drum, a charger, a cleaning unit and a black and white developing unit, and the process cartridge can be easily attached to and removed from the apparatus.
In this type of copier, the above-described process cartridge is replaced before parts and materials to be used to form an image have worn out beyond limits in order to avoid overworking the copier and to obtain a stable image quality.
In the copying machine industry, there is now an increased demand for a color image instead of a black and white image because a color image has much information. In order to meet the demand, a color copier has been disclosed in U.S. Pat. No. 4,500,195 issued to Hosono, wherein the color copier is provided with a color copy process cartridge which has a photoreceptor drum, a charger, a color developing device composed of a plurality of developing units, a cleaning unit and the like, and is provided with a black and white copy process cartridge with a black (BK) developing device so that the black and white copy process cartridge can be used as the spare of the color copy process cartridge.
However, the above-described color copy process cartridge has a complicated structure and is expensive since a plurality of developing devices are installed in it. In order to put the color copy process cartridge into practical use in terms of cost reduction, it is preferable that the above-described cartridge is replaced and discarded after its photoreceptor with long life has been used to its limits or the carrier in the developer has been used to its limits. The life of the above-described photoreceptor drum is usually 50000 to 80000 color copies and the life of the carrier contained in the developer is 20000 to 30000 color copies. Accordingly, toner is needed to be supplied from a toner supply unit provided to each of the plural apparatus, wherein each toner supply unit is corresponding to a developing unit. The toner supply unit is provided to the outside portion of the outer wall of the process cartridge and connected with the process cartridge at the connecting portion which has an opening to supply toner to the developing chamber of the developing unit.
However, in the case of the color image forming apparatus disclosed in the above-mentioned U.S. Pat. No. 4,500,195, the process cartridge must be replaced when the image forming mode is changed from the color image forming mode to the black and white image forming mode, or from the black and white image forming to the color image forming mode. Accordingly, it has the disadvantages of complicated operation, high cost, and waste of time.
There is a demand for a compact and light image forming apparatus as a printer and copier have become popular. Since the black and white image forming apparatus has been replaced with the color image forming apparatus, it has become very important to make the apparatus compact. However, in the case of the above-described color image forming apparatus disclosed in the U.S. Pat. No. 4,500,195, a plurality of developing units, a transfer means, and other image forming units are not arranged properly. Therefore, it has been difficult to make the above-described apparatus compact and to obtain a color image of stable quality.
The first example of the present invention aims to solve the problems described above. The object of the present invention is to provide a color image forming apparatus in which a color image forming process cartridge is adopted, and which is characterized in that: a color image of stable quality is obtained; the apparatus is made compact by the proper arrangement and composition of image forming units; and the image forming mode is easily converted from color image forming to black and white image forming without being restricted by a cartridge.
Furthermore, in the case of the above-described color image forming, apparatus disclosed in the U.S. Pat. No. 4,500,195, it has this disadvantage that the apparatus is stained by the toner which leaks out and dispersed when the toner supply unit is connected with the process cartridge at the connecting portion. In order to eliminate this disadvantage, a complicated sealing member to seal the connecting portion becomes necessary, wherein the sealing member is opened and closed when the toner supply unit is connected with and disconnected from the process cartridge. Especially, in the case of a color image forming apparatus, it is necessary to supply plural kinds of toner to a plurality of developing units. Accordingly, the structure becomes further complicated and even when a small amount of toner leaks out and disperses, the image quality is lowered because of color mixture caused by mixed toners.
The above-described color image forming apparatus has the further disadvantages, that color mixture tends to occur, and that it is difficult to maintain stability of the apparatus to acquire balance because a plurality of developing units stacked horizontally in the process cartridge are horizontally provided close to the photoreceptor drum. The above-described color image forming apparatus has the further disadvantage, that the transfer and conveyance means of transfer paper tends to be stained by the toner which leaks out and disperses because the means is located below the photoreceptor drum.
In order to solve the problems described above, the second example of the present invention has been offered. The object of the second example is to provide a color image forming apparatus characterized in that: the quality of a black and white image is stabilized by adopting a black and white process cartridge; the image quality is improved and the apparatus is made compact by a proper arrangement and composition of image forming units; and by providing color developing units to the apparatus the image forming mode is easily converted from the black and white copying mode to the color copying mode without restrictions of the process cartridge.
Conventionally, some types of electrostatic image forming apparatuses have been used. One is characterized in that a photoreceptor drum and a developing unit are provided to a unit which can be rapidly attached to and removed from the apparatus. The other is characterized in that a unit including a photoreceptor drum and a unit including a developing unit are individually provided to the apparatus, wherein both units can be rapidly attached to and removed from the apparatus. The above-mentioned electrostatic image forming apparatuses are formed in such a manner that the inspection of the inside of the apparatus, the exchange of parts, and the cleaning of the inside of the apparatus can be easily and positively conducted.
The life of a photoreceptor which is repeatedly used to form images, is limited. For example, the photoreceptor is generally replaced with a new one when it has been used to the limit defined as the number of times in which the photoreceptor has been used to form images, wherein the number of times can be 10000, 30000, or 50000 times. The life of a developing unit is limited in the same way as the photoreceptor. The photoreceptor is commonly replaced with a new one when it has been used to the limit.
The photoreceptor and the developing unit have the endurance limit within which an image of good quality can be formed. The endurance limit is determined by the number of times in which images have been formed. When the photoreceptor is used to the limit, it is suddenly degraded. For that reason, the photoreceptor must be replaced with a new one before it has been worn beyond the limit. In the case of a developing unit, although the endurance limits of Y, M, C, and BL developing units are the same, the frequency of use of each developing unit is different when multicolor image forming is conducted. Accordingly, each developing unit reaches the limit of use at different times. In many cases, the frequency of use of the black developing unit is high and the frequency of use of the color developing unit is not so high. In the case described above, if each color developing unit is discarded on the assumption that each color unit has worn out synchronously with the black developing unit, it will amount to discarding color developing units which still have enough capacity, which can be considered enormous losses from the view point of economical use of color developer and color developing units.
In the case of multicolor image forming, the frequency of use of Y, M, and C developers or of B, G, and R developers can be regarded as almost the same.
The third example of the object of the present invention is to provide an electrostatic image forming apparatus in order to solve the above-described problems, wherein the electrostatic image forming apparatus is characterized in that: a cartridge is provided in which the units having the same frequency of use are built so that the work of inspection, cleaning and replacing parts can be conducted precisely and easily, and furthermore the photoreceptor, the developing unit and the cleaning unit can be utilized until they wear out to the limit.